FOR THE longest time, Miss Manners could not, for the life of her, figure out how it was possible that there were more divorces being announced than marriages. Even allowing for the fact that her age group is one whose current thme is ''Why shouldn't I have the best that's available on the market?'' it seemed statistically impossible.

Then she came to realize that while one marriage announcement serves for two people, there are two divorce announcements for every divorce.

How many should there be?

None.

No, no, Miss Manners has not revoked your right to be divorced as often as you choose, although she is considering it, unless people realize that the luxury of maintaining a lifelong feud with one's former spouse, to be dramatized at the weddings of mutual children, is no longer possible.

You may even tell people that you are being divorced--useful information for those wanting to invite both of you to dinner, or to court one of you. It may be told in person or by letter, with as many details and as much emotional coloration as you think fitting, although Miss Manners strongly advises unembellished statements (just sprinkled with kind words about the parting spouse to show you are not a victim) on the grounds of dignity, privacy and the fact that bitterness and gloating are equally unattractive postures.

What you cannot do is make a mass announcement. Miss Manners has seen a variety of ghastly ones: cutesy cards, pseudo-formal ones and even form letters, offshoots of the mimeographed Christmas letters Miss Manners so despises, with a biographical sketch of the correspondent and the notation that the change of address was occasioned by the ex-spouse's stipulation that the new couple get out of sight.

Really, this is not quite tasteful, is it? Surely if you purport to tell the whole story, the quality of the original couple's intimate life should be included, too, along with the superior attractions of the newcomer. (Miss Manners is just kidding. It's probably only a matter of time until someone does that.)

The fact is that few of life's events, no matter how significant, are the subjects of formal announcements. You do not send cards announcing pregnancies, engagements or deaths, and Miss Manners does not really approve of them for births, either. All these things may be told, and may slip into the newspapers with some help from the interested parties, but do not get themselves done up in engraved announcements or the equivalent. The pretense is that you are telling individuals, individually.

The model that is being used for divorce announcements is, not surprisingly, the marriage announcement (as distinct from the formal invitation to a wedding, or other ceremony or related reception).

Miss Manners has analyzed this incorrect impulse as part of the widespread yearning for the trappings of marriage that arose the minute that respectable society no longer insisted on a couple's entering and maintaining wedlock.

It is always the unmarried couples who insist on being treated as socially inseparable. Unmarried couples are demanding legal rights of all kinds. Whatever happened to "We don't need a piece of paper"? Miss Manners may not have endorsed free love, but she does think it silly and mean to deprive it of its freedom.

In any case, the forms of marriage, including the announcement, do not apply to other occasions, as there is nothing exactly like marriage. Divorcing people should know that. MISS MANNERS RESPONDS

Q. A very dear friend of my husband's and mine, who was best man at our wedding, has a "lady" friend whom I do not particularly like. This is not the problem, since although I do not like Miss L. or enjoy her company, I always try to be polite and am able to tolerate her for short periods of time.

The problem: Miss L. engages Mr. B. in public displays of affection that I find quite embarrassing. I do not object to an occasional peck on the cheek, or even on the lips, but Miss L. kisses Mr. B. passionately, accompanied by fondling and caressing, for a full five minutes (I once checked by watch) in the presence of company.

Once I thought perhaps Mr. B. had experienced a silent heart attack that no one else had noticed, but having taken a CPR course, I know she was not using proper technique. It also has occurred to me that this might be an obscure form of epilepsy, but that seems unlikely.

There is no warning as to when an attack may occur, so one may not leave the room ahead of time; and such behavior is difficult to simply ignore in a small gathering of four to six people.

My husband suggests I excuse myself and leave the room. He himself sits and looks at the ceiling. Another friend once exclaimed, "Boy! I'm getting horny!" during such a display, but this seemed to have no effect on Miss L., and anyway, such exclamations are not my style. I should tell you that Mr. B. sits or stands passively throughout the affair--he does not seem like an active participant, but neither does he try to fight her off.

I am in a quandary as to how to let Miss L. know the rudeness of her behavior without being rude myself, offending Mr. B. or making others more uncomfortable than they already are.

A. Ah, to let someone know that she has been rude, without being rude oneself! That is one of the trickiest social skills one can acquire, and certainly one of the most useful.

You know that Miss Manners does not allow you to tax people directly with their rudeness, itself a greater rudeness. But she does not forbid you to show your polite and compassionate concern for a friend.

The other onlooker's crude remark will not do at all; neither will your husband's technique of refusing to look on. Public displays of affection are not generally made, as the performers allow one to suppose, because there are no private facilities available, or because the passion is utterly uncontrollable. They are made in order to demonstrate to others that the passion is utterly uncontrollable. In other words, the idea is to show off and arouse a bit of envy in others. The reactions you describe are therefore the desired ones.

What you must do, instead, is to fail to perceive that anything enviable is going on. You have yourself suggested a solution in your humorous description of your thoughts; you just haven't carried it far enough.

Suppose, rather than keeping these thoughts to yourself, you leapt out at the embracing couple, screaming at him, "Are you all right?" and at her, "What can I do to help?" That should startle them enough right there to stop the proceedings.

When they recover enough to insist that nothing is the matter, you keep up a stream of babble along the lines of "Oh, thank God, I thought he was having a heart attack--or that it was some kind of epilepsy--you can't be too careful with these things, and I was worried because he looked so frightened."

Then switch to puzzlement. "Well, then, what were you doing?" If they should go so far as to answer that one--Miss Manners imagines them crimson-faced by now, looking for a way to end this unfortunate scene--you reply, "Oh, okay, I guess. Would you like to go upstairs or something?"

Miss Manners promises you that you will only have to play this scene once. And it will be nothing to the scene that is played when Mr. B. gets Miss L. out to the car, which is not likely to be a love scene.